1. Field of the Invention
This invention relates generally to regional anesthesia and more particularly to a system for positioning a catheter and nerve stimulator needle in conjunction with various procedures, such as, the administration of an anesthetic blockade and for continuous infusion of anesthetic or analgesic through the catheter.
2. Antecedents of the Invention
The field of regional anesthesia relates to the practice of administering anesthesia to a specific body region during surgery, for the relief of postoperative pain, and for extended relief of trauma or chronic pain. Often, regional anesthesia has been found to be preferable to general anesthesia because of increased safety, the availability of postoperative pain control and decreased anesthetic costs.
Regional anesthesia delivery techniques strove to optimize administration of a local anesthetic in close proximity to a target or nerve plexus so as to establish a neural blockade. Successful administration of regional anesthesia was dependent upon the accurate placement of the anesthetic in relation to the target nerve or nerves.
Various techniques have been employed to assist in placement of an administration needle in close proximity to the target nerve, which was not externally visible. One of the traditional methods of needle placement involved eliciting paresthesia. Among the disadvantages of this technique was the lack of accurate patient responses amongst patients who were disoriented and/or sedated.
A prevalent technique employed the use of nerve stimulators electrically coupled to a nerve stimulator needle. Such method was premised upon the phenomenon that an electrical pulse is capable of stimulating a motor nerve fiber to contract an innervated muscle or cause paraesthesia, in the case of sensory nerve stimulation.
The nerve stimulator needle was placed within the tissue of the patient's body in the vicinity of the nerve to be blocked and then advanced until stimulation of the target nerve was achieved as determined by visually detecting muscle contractions or by eliciting a report that the patient felt the stimulus in response to the current flow through the stimulator needle.
The current supplied by the nerve stimulator was reduced as the nerve stimulator needle was further advanced, until stimulation of the target nerve was achieved using a reduced current level associated with a prescribed distance between the needle tip and the target nerve.
Thereafter, a portion of the anesthetic dose was administered through the needle to terminate the response to the nerve stimulation current. If the response was terminated by the initial administration, the needle was deemed to be properly positioned in proximity to the target nerve and the remaining dose of anesthetic was administered and the needle was withdrawn upon completion of the surgical procedure.
Placement of catheters for continuous infusion of local anesthetics or other drugs during surgical procedures and primarily postoperatively has been achieved by use of an intra-catheter which was placed or threaded through the internal lumen of a larger needle or stiff cannula, or by use of an extra-catheter which was placed or threaded over an internal needle or smaller stiff cannula. Each technique has been associated with certain disadvantages and limitations that have resulted in less than optimal results for achieving successful continuous plexus or nerve block in clinical practice. These disadvantages have severely limited the use of continuous anesthesia or analgesia, resulting in under-utilization of continuous techniques in favor of more predictably successful, less invasive and usually less traumatic and therefore safer nerve or plexus blockade utilizing only a nerve stimulation needle for anesthesia or analgesia administration as previously described.
Problems associated with the use of an intra-catheter included the fact that a very large (and therefore more traumatic) introducing needle (e.g. 17 or 18 gauge) was necessary to allow passage of a smaller (usually 19 or 20 gauge) flexible catheter. This caused increase pain and discomfort during the placement. After needle placement, the catheter was passed through the bore of the introducing needle. This technically difficult step could cause movement of the needle tip. Additionally, there was little control of the final position of the distal end of the catheter because the flexibility of the catheter did not allow the practitioner to accurately determine the position of the distal end of the catheter after it passed beyond the needle tip.
Stimulating catheters have been developed with a flexible metal stylet inside the catheter which allowed for the ability to electrically stimulate the nerve or nerves, but these too, were difficult to control in terms of the final positioning of the catheter tip once it passed beyond the needle tip.
Another problem with intra-catheter systems has been persistent leaking of the injected medication at the skin entry point of the removed introducing needle. This occurred because the catheter diameter was smaller than the needle diameter and the diameter of the opening left by the introducing needle. Leakage was especially pronounced after placement of continuous catheters for superficial nerves or nerve plexus.
Major problems associated with the use of an extra-catheter system included the fact that extra-catheters have had to be made of larger gauges than desirable and have been stiffer than desirable to allow adequate stability for advancement over the smaller internal needle. The employment of stiff catheters near nerves for continuous infusion of anesthetics or analgesic medications was undesirable. The stiff catheters could result in nerve trauma.
Smaller, softer and more flexible catheters were preferable for procedures involving continuous infusion. A catheter with the desired flexibility and small diameter was difficult to pass or thread over the needle due to undesired buckling or bending, however. The length of the extra-catheter was therefore limited because longer extra-catheter systems of very small diameter were too flexible and therefore unstable and difficult to pass.
The longer a thin catheter or thin needle was, the more unstable it was. This was because each additional unit of length compounded its flexibility. Such catheters would bend when advanced through the skin and deeper tissues, making targeted accurate placement difficult. Additionally, extra-catheters were required to freely slide off of the internal needle, cannula, or stylet and therefore often had undesired movement in relation to the internal needle during use, especially upon advancement and withdrawal. If the extra-catheter was more tightly fitted to the internal needle, withdrawal of the stylet or needle often put undue traction on the catheter, resulting in undesired movement of the catheter tip from the optimal position that was already achieved.